The risks involved in the operation of hazardous waste sites have been chronicled in the popular media from movies, to books to newspapers. We are all too familiar with the dangers of being exposed to hazardous and/or toxic waste hereafter (collectively referred to as xe2x80x9chazardous wastexe2x80x9d) from such sites. Concerned about the public""s health, both government and industry have sought to develop ways to safely destroy such hazardous waste.
One of the most commonly accepted ways to destroy hazardous waste is by using an incinerator. Incinerators have their drawbacks, however. Unfortunately, incinerators are not capable of destroying certain types of hazardous waste such as polychlorinated biphenyls, asbestos, heavy metal sludges, complex organics and pesticide waste. Incinerators generate their own hazardous waste byproducts, such as toxic ash, when processing hazardous waste.
Some have attempted to develop xe2x80x9cpyrolyticxe2x80x9d or xe2x80x9cpyrolysis-basedxe2x80x9d systems (i.e., systems which destroy, process and handle waste in an oxygen reduced atmosphere to avoid burning or combustion) (hereafter referred to as xe2x80x9cpyrolytic systemxe2x80x9d) as an alternative to incineration. One such system is disclosed in U.S. Pat. No. 5,534,659 to Springer, et al (xe2x80x9cSpringerxe2x80x9d).
In general, Springer discloses the use of a xe2x80x9cplasmaxe2x80x9d torch in a pyrolytic system. Because plasma torches can be used to generate extremely high temperatures in an oxygen reduced atmosphere, they are capable of destroying, through pyrolysis, hazardous material which cannot be destroyed by incineration.
However, attempts to build or use existing pyrolytic systems or methods have not proven to be safe or successful (xe2x80x9cexistingxe2x80x9d means systems, methods or devices other than those discovered by the present inventors). Moreover, attempts to practice the ideas embodied in some existing systems and methods have proven to be downright dangerous.
It has been determined through experimentation that existing pyrolytic systems and methods fail to appreciate the need for xe2x80x9creal-timexe2x80x9d controls over each step in the destruction, processing and handling (collectively referred to as xe2x80x9cprocessingxe2x80x9d) of hazardous waste. It has long been known that the pyrolytic destruction of hazardous wastes generates flammable and potentially explosive byproducts, such as carbon monoxide or hydrogen.
Experimentation using existing systems and methods, such as the one disclosed in Springer, revealed flaws and safety issues in their processing and control systems.
Pyrolytic waste processing systems which do not have effective, automatic controls are unsafe to operate. Only automatic controls which react rapidly or almost instantaneously can operate quickly enough to react to changes taking place within the system.
Many changes may occur within a pyrolytic system which, if not adequately controlled, may make the system unsafe to operate. One source of concern are changes in the ratio of oxygen to product gas within the system. More specifically, the fluctuation of the concentration of oxygen in a flammable product gas stream is of great concern. A number of things may cause the concentration of oxygen to fluctuate. First, a particular type of hazardous waste (e.g., medical waste) may comprise a number of different constituents. For example, medical waste comprises a combination of cloth, paper, cardboard, plastic, solvents, metal and/or glass. When each of these constituents is fed into a waste processing system, different types and amounts of byproduct gasses (xe2x80x9cproduct gassesxe2x80x9d) are released as they are processed. As a result, the ratio of oxygen to product gas (by volume) within the system may fluctuate, sometimes rapidly.
If the ratio is not closely monitored and rapidly controlled, the ratio may exceed safe levels and an explosion may occur.
Second, a similar situation occurs when more than one type of hazardous waste is destroyed. For example, hazardous waste can be separated into organic and inorganic wastes (e.g., petrochemicals and asbestos). In general, organic wastes release different types and amounts of product gas compared to inorganic wastes. If the same pyrolytic waste processing system is used to destroy both inorganic and organic wastes, the different product gasses released by each type of waste will also tend to make the ratio of oxygen to product gas within the system fluctuate, sometimes widely and rapidly, as well.
In order to safely operate hazardous waste processing systems, such rapid fluctuations must be controlled very quickly.
Accordingly, it is desirable to provide methods and systems for safely processing hazardous waste.
It is further desirable to provide methods and systems for safely processing hazardous waste which take into account the rapid fluctuations in an oxygen to product gas ratio throughout an entire waste processing system.
Other desires will become apparent to those skilled in the art from the following description taken in conjunction with the drawings and claims.
In accordance with the present invention, there are provided methods and systems for safely processing hazardous waste undergoing pyrolysis. Such systems comprise a gas supply control unit adapted to switch a supply of gas from air to a sufficient amount of an inert gas, such as nitrogen, to a plasma arc torch, and supply a sufficient amount of an inert gas to a processing vessel, prechamber, feed chamber and other points in the system where air may enter the system; a waste feed control unit adapted to control a supply of waste to the processing vessel to help maintain the ratio; a pressure balancing control unit adapted to control pressures in the system; and an interlocking control unit adapted to halt operations within the system to protect against flame propagation.
Under certain circumstances, the gas supply control unit and waste feed control unit can be adapted to operate simultaneously.
While the gas supply and waste feed control units are adapted to regulate the amount of inert gas or waste fed into a system, the pressure balancing control unit is adapted to regulate the amount of gas pressure within the system by, for example, adjusting fan dampers.
Other novel systems envisioned by the present invention comprise gas supply lines adapted to inject a sufficient amount of an inert gas into components of the system in order to maintain a safe oxygen to product gas ratio.
Besides the systems described above, the present invention also envisions methods and programmed mediums (e.g., devices which store computer programs and/or code) adapted to control and carry out substantially the same features and functions.
The present invention and its advantages can be best understood with reference to the drawings, detailed description of the invention and claims that follow.